1. Field of the Invention
This invention relates generally to a copying or printing apparatus, and more particularly, it relates to the heat and pressure fixing of particulate thermoplastic toner by direct contact with a heated fusing member in a xerographic environment. Even more particularly this invention relates to a multi-position fuser cam to compensate for fuser nip pressure over a large range of paperweights.
The basic design of the multi-position fuser cam (lobe) in accordance with the embodiment described herein will help compensate fuser nip pressures over a large range of paperweights. Each cam position will yield a higher nip pressure, ideally not more than 0.4 mm nip increase per lobe. This will lessen the need to raise and lower fuser temperature and will allow higher throughput speeds. This will also increase fuser roll and belt life.
2. Description of Prior Developments
In the process of xerography, a light image of an original to be copied is typically recorded in the form of a latent electrostatic image upon a photosensitive member with subsequent rendering of the latent electrostatic image visible by the application of electroscopic marking particles, commonly referred to as toner. The visual toner image can be either fixed directly upon the photosensitive member or transferred from the photosensitive member to another support, such as a sheet of plain paper, with subsequent affixing of the toner image thereto in one of various ways, for example, as by heat and pressure.
In order to affix or fuse electroscopic toner material onto a support member by heat and pressure, it is necessary to elevate the temperature of the toner material to a point at which the constituents of the toner material coalesce and becomes tacky while simultaneously applying pressure. This action causes the toner to flow to some extent into the fibers or pores of support members or otherwise upon the surfaces thereof. Thereafter, as the toner material cools, solidification of the toner material occurs causing the toner material to be bonded firmly to the support member. In both the xerographic as well as the electrographic recording arts, the use of thermal energy and pressure for fixing toner images onto a support member is well known.
One approach to heat and pressure fusing of electroscopic toner images onto support members has been to pass the support members with the toner images thereon between a pair of opposed roller members, at least one of which is internally heated. During operation of a fusing system of this type, the support members to which the toner images are electrostatically adhered are moved through a nip formed between the roller members with the toner images contacting a fuser roll thereby to effect heating of the toner images within the nip.
Belt fusers are known in the prior art. For example, U.S. Pat. Nos. 4,563,073 and 4,565,439 each disclose a heat and pressure fusing apparatus for fixing toner images. The fusing apparatus is characterized by the separation of the heat and pressure functions such that the heat and pressure functions are effected at different locations on a thin flexible belt forming a toner contacting surface. A pressure roll cooperates with a stationary mandrel to form a nip through which the belt and a copy substrate pass simultaneously. The belt is heated such that by the time it passes through the nip its temperature together with an applied pressure is sufficient for fusing the toner images passing therethrough.
Especially with the introduction of color copying or color printing apparatus, issues have been raised within the fusing areas due to the use of different types and thickness of paper stock. Current methods used for heavy-weight paper stock in such process or apparatus is to adjust the temperature of the fuser and/or slow the speed of the fuser in a downward direction. The problems raised with this procedure is that the process does not take into account the thickness of the paper stock which has a proportional effect on a fuser nip. This in turn causes the paper stock to ripple which prevents the paper stock from tacking properly which in turn causes deletion problems when duplexing.
Current designs for a fuser assembly especially useful for accommodating heavier papers, seem to be favoring increasing the fusing temperature and/or slowing the paper speed through the fuser assembly. However, slowing the speed takes away from overall productivity, and additional heat has a negative effect on soft roll life. A multi-lobed cam concept in accordance with the features of the present invention could be used in conjunction with current fuser assembly designs to enhance fusing characteristics, or in some cases even replace current fuser assembly designs. The invention as described herein offers several benefits over current fuser assemblies, i.e., increased throughput speeds, wider latitude of materials, longer fuser roll life, and overall improvement in the condition of output pages by further minimizing curl and/or wrinkling.
According to the features of the embodiments described herein, the above described disadvantages found within a fuser environment are avoided including the avoidance of overheating of the paper, by using a roll fusing apparatus for effectively heating and fusing quality toner images on various different thicknesses of substrates including a frame; a heated fuser roller having a first end and a second end respectively mounted to the frame; a pressure means mounted to the frame and forming a fusing nip with the heated fuser roller, the heated fuser roller and the pressure means being movable for receiving, heating and applying a nip force to toner images being moved through the fusing nip on various different thicknesses of substrates; a rotatable cam providing a varying amount of pressure to the pressure means in response to the thickness of the substrate being fed into the nip of the fusing apparatus; means for rotating the cam; and control means for selectively moving the cam in response to the thickness of the substrate.
Included within the scope of the features of the present invention which have overcome the disadvantages of the prior art are an electrostatographic reproduction machine including a movable image bearing member having an image bearing surface defining a path of movement therefor; electrostatographic devices mounted along the path of movement for forming and transferring toner images onto various different types of substrates; and a roll fusing apparatus for effectively heating and fusing the toner images on various different thicknesses of substrates, the roll fusing apparatus including: (i) a frame; (ii) a heated fuser roller having a first end and a second end respectively mounted to said frame; (iii) a pressure means mounted to said frame and forming a fusing nip with the heated fuser roller, the heated fuser roller and the pressure means being movable for receiving, heating and applying a nip force to toner images being moved through the fusing nip on various different thicknesses of substrates; (iv) a rotatable cam providing a varying amount of pressure to the pressure means in response to the thickness of the substrate being fed into the nip of the fusing apparatus; (v) means for rotating the cam; and (vi) control means for selectively moving the cam in response to the thickness of the substrate.